Used anonymous func for rank wrapper

Author: WillAyd

pandas/core/groupby.py

@@ -2172,15 +2172,6 @@ def get_group_levels(self):
     # ------------------------------------------------------------
     # Aggregation functions
 
-    def _group_rank_wrapper(func, *args, **kwargs):
-        # Need to explicity unpack *args to support Py < 3.5
-        # See PEP 448
-        return func(args[0], args[1], args[2], args[3],
-                    kwargs.get('ties_method', 'average'),
-                    kwargs.get('ascending', True),
-                    kwargs.get('pct', False),
-                    kwargs.get('na_option', 'keep'))
-
     _cython_functions = {
         'aggregate': {
             'add': 'group_add',
@@ -2207,7 +2198,12 @@ def _group_rank_wrapper(func, *args, **kwargs):
             'cummax': 'group_cummax',
             'rank': {
                 'name': 'group_rank',
-                'f': _group_rank_wrapper
+                'f': lambda func, a, b, c, d, **kwargs: func(a, b, c, d,
+                        kwargs.get('ties_method', 'average'),
+                        kwargs.get('ascending', True),
+                        kwargs.get('pct', False),
+                        kwargs.get('na_option', 'keep')
+                )
             }
         }
     }